Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
With the proliferation of various wireless technologies including wireless local area networks, wide area networks, cellular telephone systems, etc., demand for wireless spectrum suitable for wireless communications networks has grown substantially. The demand is expected to accelerate even more in the near future because of exponential growth in wireless broadband data network traffic. While government agencies charged with spectrum allocation and management such as the Federal Communications Commission (FCC) in the U.S. institute policies aimed at identifying additional spectrum that can be devoted to wireless networks, and in particular to broadband networks, implementation of these policies is generally constrained by factors like the range of available/practical frequencies.
Despite measures aimed at freeing useful spectrum, the demand for wireless bandwidth for broadband services is virtually certain to exceed spectrum being made available. One of the considerations in addressing this challenge is whether wireless networks, and in particular wireless broadband networks, could effectively operate on spectrum that is nominally assigned to other applications without significantly interfering with or otherwise disrupting those “primary” applications. Further consideration may be given to the practicality of such “secondary” operation of wireless broadband networks on spectrum that is shared not only with a “primary” application but with other “secondary” applications as well. Consideration may also be given to the practicality of broadband wireless networks operating as “primary” users of a particular block of spectrum with the caveat that some accommodation of secondary users is required.
Despite the enabling properties of network control of frequency use, spectrum flexibility, and cognitive radio systems, there remains a substantial impediment to wireless broadband use of spectrum on a co-primary or secondary basis. The challenge is that in many cases other primary or secondary applications may involve either low power transmissions intended for relatively short range communications or highly directional transmissions intended for point-to-point communications. Such communications links may be compromised due to severe interference from co-frequency transmissions from a nearby high power wireless network base station or from user devices being served by a wireless network base station. Those transmissions may be the result of the base station being unable to detect, for purposes of interference avoidance, the very low power or very directional transmissions from co-spectrum communications systems. Conversely, since the specific frequencies being employed by a given high power wireless network base station and the user devices it serves may change frequently and without warning, such transmissions may significantly interfere with the operations of co-spectrum low power or directional systems despite procedures (automatic or manual) whereby “locally unoccupied” channels are identified for use by those systems.
Thus, conventional systems do not allow relatively high power broadband networks of essentially ubiquitous coverage and the user devices operating therein, to coexist with the simultaneous operation of lower powered, short range communications devices and systems within that coverage and sharing the same general frequency bands. Such systems fail to manage the spectrum occupation of the network on a shared frequency band in a manner so that it does not interfere excessively with, or be excessively interred with by, various low power co-users of that band.